var globalAudioContext = new webkitAudioContext();

function morsecode(text, unit, freq) {
	'use strict';

	// defaults
	unit = unit ? unit : 0.05;
	freq = freq ? freq : 700;
	var cont = globalAudioContext;
	var time = cont.currentTime;

	// morsecode
	var code = {
		a: '._',    b: '_...',  c: '_._.',  d: '_..',   e: '.',     f: '.._.',
		g: '__.',   h: '....',  i: '..',    j: '.___',  k: '_._',   l: '._..',
		m: '__',    n: '_.',    o: '___',   p: '.__.',  q: '__._',  r: '._.',
		s: '...',   t: '_',     u: '.._',   v: '..._',  w: '.__',   x: '_.._',
		y: '_.__',  z: '__..',  0: '_____', 1: '.____', 2: '..___', 3: '...__',
		4: '...._', 5: '.....', 6: '_....', 7: '__...', 8: '___..', 9: '____.'
	};

	// generate code for text
	function makecode(data) {
		for (var i = 0; i <= data.length; i ++) {
			var codedata = data.substr(i, 1).toLowerCase();
			codedata = code[codedata];
			// recognised character
			if (codedata !== undefined) {
				maketime(codedata);
			}
			// unrecognised character
			else {
				time += unit * 7;
			}
		}
	}

	// generate time for code
	function maketime(data) {
		for (var i = 0; i <= data.length; i ++) {
			var timedata = data.substr(i, 1);
			timedata = (timedata === '.') ? 1 : (timedata === '_') ? 3 : 0;
			timedata *= unit;
			if (timedata > 0) {
				maketone(timedata);
				time += timedata;
				// tone gap
				time += unit * 1;
			}
		}
		// char gap
		time += unit * 2;
	}

	// generate tone for time
	function maketone(data) {
		var start = time;
		var stop = time + data;
		// filter: envelope the tone slightly
		gain.gain.linearRampToValueAtTime(0, start);
		gain.gain.linearRampToValueAtTime(1, start + (unit / 8));
		gain.gain.linearRampToValueAtTime(1, stop - (unit / 16));
		gain.gain.linearRampToValueAtTime(0, stop);
	}

	// create: oscillator, gain, destination
	var osci = cont.createOscillator();
	osci.frequency.value = freq;
	var gain = cont.createGainNode();
	gain.gain.value = 0;
	var dest = cont.destination;
	// connect: oscillator -> gain -> destination
	osci.connect(gain);
	gain.connect(dest);
	// start oscillator
	osci.start(time);

	// begin encoding: text -> code -> time -> tone
	makecode(text);

	// return web audio context for reuse / control
	return cont;
}